Vim: src/*.sh scripts fix + enhancements

src/dsm-control.sh:
	- Add simple check for "status" + appropriate return codes
	- Fix "log" return code to non-error state

src/installer.sh:
	- Add "vimdiff" symlink into /usr/local/bin
	- Alter /bin/vi symlink from "busybox" to "vim-utf8" when Vim package is installed